Method for correcting structure-size-dependent positioning errors in photolithography

ABSTRACT

A method for correcting structure-size-dependent positioning errors during the photolithographic projection by an exposure apparatus and the use thereof includes providing an exposure apparatus for exposing a plurality of exposure fields and a simulation model of the exposure apparatus for specifying correction values for intra-field errors, providing a first pattern with first structure elements and first measurement marks, which, in the case of a projection, are beset by a first positioning error and a second positioning error dependent on the dimensions and the position in the exposure field, providing a correction function suitable for specifying the first and the second positioning error, determining an average relative positioning error including the first and the second positioning error, calculating correction values for the control of the exposure apparatus, and transmitting the correction values to the exposure apparatus so that subsequent exposures are performed with an improved overlay.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119 to GermanApplication No. DE 10 2004 037018.4, filed on Jul. 30, 2004, and titled“Method for the Correction of Structure-Size-Dependent PositioningErrors During the Photolithographic Projection by Means of an ExposureApparatus and the Use Thereof,” and to German Application No.102004063522.6, filed on Dec. 30, 2004, and titled “Method for theCorrection of Structure-Size-Dependent Positioning Errors During thePhotolithographic Projection by Means of an Exposure Apparatus and theUse Thereof,” the entire contents of each are hereby incorporated byreference.

FIELD OF THE INVENTION

This invention relates to a method for the correction ofstructure-size-dependent positioning errors during the photolithographicprojection by an exposure apparatus, and to using such a method forlithographic patterning of a semiconductor wafer.

BACKGROUND

In order to fabricate integrated circuits, layers provided withdifferent electrical properties are usually applied to semiconductorwafers and patterned lithographically. A lithographic patterning mayinclude applying a photosensitive resist, exposing the resist with adesired structure for the relevant layer, developing the resist, andsubsequently transferring the resist mask thus produced into theunderlying layer in an etching step.

As the integration densities of integrated circuits continuouslyincrease, positional accuracy requirements of a structure to beprojected onto the semiconductor substrate also increase. Whenpreliminary layers have already been transferred in underlying layers,e.g., in a lithographic projection step, it is necessary to account forstricter tolerance limits with regard to the mutual orientation of thestructure to be projected onto the substrate relative to the structuresof the aforementioned preliminary layers to ensure functionality of thecircuit.

Dense line-space patterns are formed, for instance, in the area offabrication of dynamic random access memories (DRAM) with line widths of70, 90, or 110 nm, for example, in the region of the first circuitlayers. In modem technologies for DRAM fabrication, the accuracyrequired for the orientation of two structures, also referred to as theoverlay budget, will decrease due to decreasing structure resolutions.Thus, for example, the tolerable positional inaccuracy is onlyapproximately 20 nm in the case of the 100 nm process line. Current andfuture process lines are thus sensitive to errors in the positionalaccuracy.

For the lithographic projection step, which may be performed, e.g., in awafer stepper or scanner, alignment sequences are therefore providedbefore the beginning of the respective exposures. The alignment marksare typically arranged in the edge regions of the masks providing therelevant structure. During the exposure, the alignment marks aretransferred in the sawing frame separating the individual exposurefields on the wafer. The alignment marks make it possible to determinethe position of the structures formed on the wafer, or, as a result ofdetermining the position of the alignment marks, possible to deduce theaccurate positioning and orientation of the structure for the integratedcircuit.

The exposure of the individual exposure fields is usually performed suchthat the top side of the semiconductor wafer is subdivided into apattern of exposure fields in the form of a matrix or grid and issuccessively exposed by the wafer scanner or the wafer stepper.

The positional accuracy of two layers lying one above the other isnormally determined by overlay targets during the production ofintegrated circuits. The targets are two partial structures each imagedseparately onto each of the layers. The first partial structure maycomprise a rectangular structure element surrounded by a frame-typesecond partial structure. Overlay targets are usually arranged togetherwith other alignment marks in the sawing frame region. The structuredescribed above is known as a box-in-box mark or a box-in-frame mark.The offset of the individual partial structures with respect to oneanother is usually measured by an overlay measuring apparatus, forexample, an optical microscope.

In the exposure of a semiconductor wafer by a wafer scanner, a number ogeffects may lead to overlay errors. These overlay errors can generallybe assigned to two categories of error sources. First, errors may occurwhich arise during the exposure within an exposure field. These errorsources are usually referred to as intra-field error or field error.Second, error sources may be caused by the division of the semiconductorwafer into individual exposure fields and may be different for eachexposure field. These error sources are usually referred to asinter-field error or grid error.

The orientation or alignment of the substrate in the exposure apparatuswith respect to the projection optical arrangement (i.e., the projectionlenses, the respective mask to be projected, apertures, and theillumination source, etc.) is carried out by comparing the alignmentmarks with reference marks. Such reference marks are often inserted bythe lens system with respect to a detector.

The way the alignment method (alignment or overlay) is specificallycarried out depends on the apparatus manufacturers. Based on the markcomparison, an offset between the actual alignment mark position and theideal position of the reference mark is ascertained, modeled, andcorrected.

A problem to which little consideration has been given hitherto is thedegree of positional accuracy of different structure pattern portions,which can be attained differently within an exposure field. Reasons forthis are, in particular, lens imaging errors such as, for example, thedistortions called coma, three-leaf clover, astigmatism, etc., which aregenerally referred to as aberration errors.

One problematic effect is that the size of the imaging error of astructure is dependent on the respective form, orientation, and size ofthe structure. Thus, for example, dense line-space structures with verysmall structure dimensions are provided with a different offset withrespect to an ideal position in an exposure with a perfect lens than,for example, the alignment marks that generally have very largedimensions.

In such cases, the above-mentioned deduction of the positions of therespectively imaged structures from the position determined for thealignment mark during the alignment and the determination of the overlaymay be erroneous. This holds true as the structures or structureelements differ from the alignment marks in size, form, and orientation.

In the area of the alignment methods, i.e., in the case of the alignmentor overlay of a wafer in the exposure apparatus, overlay measurementmarks with a microstructure are known. The microstructure is providedwith structure elements representing the semiconductor component of thislayer. The overlay measurement marks are thus subject to a differentimaging error due to lens distortions than hitherto customary box-in-boxor box-in-frame measurement marks. The exposure position determined byalignment mark comparison during the alignment of a substratesubsequently exposed is corrected such that the structures of theindividual layers, instead of the overlay measurement marks, are imagedon one another with higher accuracy.

In this case, however, it proves disadvantageous for a determination ofthe positional accuracy error by the micro-patterned measurement marksfor different structures. It is necessary to provide special measurementmarks which permit a determination of the overlay or of the positionalinaccuracies for the two layers lying one above the other. As a result,the determination of the positional inaccuracies for all layers of theintegrated circuit, particularly in an evaluation of a new process line,is very time-consuming. In conventional measuring apparatuses, thefrequently changing patterning are associated with varying contrast orintensity conditions, which impedes the measurability of themicro-patterned measurement marks.

Therefore, a method for an integrated circuit with one or a plurality oflayers that enable a simple correction of the structure-dependentpositioning errors for each layer is desirable.

SUMMARY

A method for correcting structure-size-dependent positioning errorsduring the photolithographic projection by an exposure apparatusincludes providing an exposure apparatus for performing an exposure in aplurality of exposure fields, providing a simulation model of theexposure apparatus, providing a first pattern having a plurality offirst structure elements and a plurality of first measurement marks,photolithographically projecting the first pattern by the exposureapparatus into the exposure fields, providing a correction function forspecifying the first positioning error and the second positioning error,determining an average relative positioning error including the firstpositioning error and the second positioning error, calculatingcorrection values for the control of the exposure apparatus based on thefirst positioning error and the second positioning error by thesimulation model, and transmitting the correction values to the exposureapparatus, so that subsequent exposures are performed with an improvedoverlay. The simulation model includes a calculation specification andspecifies correction values for intra-field errors during the exposure.In the case of projection by the exposure apparatus, the first structureelements are beset by a first positioning error depending on thedimensions of the first structure elements and the position of the firststructure elements in the exposure field. The first measurement marksare beset by a second positioning error depending on the dimensions ofthe first measurement marks and the position of the first measurementmarks in the exposure field. Different positioning errors are broughtabout for the first structure elements and first measurement marks dueto different dimensions as a result of aberration.

In the present invention, error contributions are determined bystructure-size-dependent positioning errors, which have the same valuein each exposure field, between the structure elements and themeasurement marks. While conventional overlay inspection methodsprimarily optimize the position of the measurement marks of differentlayers, according to the invention the structure-size-dependentpositioning error (referred to hereinafter as positioning error) of thepositionally critical structure elements and the positioning error ofthe measurement marks are determined individually and independently ofone another. The relative positioning error is returned to the exposureapparatus as an additional intra-field error, so that this contributionis corrected in subsequent exposures. The relative positioning error isprincipally caused by a projection lens of the exposure apparatus andhas an identical value given identical exposure conditions for eachexposure field. Consequently, the method according to the invention canbe carried out once up to a possible change in the exposure conditions.The calculated correction values are transmitted to the exposureapparatus and bring about a correction of the lens-induced errors.

In a further embodiment, providing the first pattern includes the firststructure elements having minimal dimensions of 100 nm or less.

Modern production processes have minimal structure dimensions of lessthan 100 nm. These critical dimensions are different from the dimensionsusually used for measurement marks, so that the invention can correctthe structure-size-dependent positioning errors particularly in moderntechnologies with very small dimensions.

In a further embodiment, providing the first pattern includes the firstmeasurement marks having minimal dimensions of between 0.5 μm and 5 μmand form the first part of an overlay target.

Overlay targets often include box-in-box or box-in-frame structuresdetected and measured by an optical microscope. The dimensions of themeasurement marks forming the overlay target are usually chosen in theregion of a few micrometers, which enables a simple detection and doesnot cause an excessively large area requirement. Due to differentdimensions with respect to the first structure elements, however, thefirst positioning error and the second positioning error are different.

In a further embodiment, providing the first pattern includes providinga sawing frame surrounding the first pattern, and providing theplurality of first measurement marks arranged such that a respectivefirst measurement mark lies in the region of each corner of the sawingframe.

Overlay targets are often accommodated in the sawing frame region and,particularly, in the region of each corner of the sawing frame aroundthe first pattern, which represents, for example, an integrated circuitto be fabricated. In accordance with this procedure, there is no need toreserve any area in the region of the first pattern, i.e., for example,in the region of the active chip area, for the measurement marks.

In a further embodiment, providing the first pattern furthermoreincludes providing the plurality of first measurement marks arrangedsuch that at least one first measurement mark lies in the region of themidpoint of the exposure field.

To be precise about the size of the positioning error within an exposurefield, at least one measurement mark is arranged within the exposurefield. In accordance with this procedure, the first and secondpositioning errors that depend on the position within the exposure fieldcan be determined with greater accuracy.

In a further embodiment, providing the correction function includesproviding a test substrate with a resist layer on the front side,providing a first test mask with a first test pattern with a firstmultiple arrangement of a first test structure, transferring the firsttest pattern by photolithographic projection into the resist layer ofthe test substrate, and determining the values of the first positioningerror of the first pattern relative to the at least one firstmeasurement mark and the at least one first micro-patterned alignmentmark for each element of the first multiple arrangement. The first teststructure includes parts of the first pattern, the plurality of firstmeasurement marks, and at least one first micro-patterned alignmentmark.

In accordance with this procedure, the first and second positioningerrors are determined relative to a micro-patterned alignment mark. Thisdetermination may be effected for a plurality of positions on theexposure field, so that the first and second positioning errors can bedetermined with great accuracy within the exposure field. The multiplearrangement with the first test structure can be measured in a simplemanner since, in particular, there is no need to take into considerationthe electrically functional circuit that is actually to be formed. Thetest structure is optimized with regard to relatively simplemeasurability and permits relatively accurate and precise determinationof the first and second positioning errors.

In a further embodiment, the exposure apparatus is a wafer scanner. Anexposure apparatus has good resolution, particularly in the patterningof layers with a high structure resolution, and thus be used for thecorrection of structure-size-dependent positioning errors of verycritical layers. During the exposure of the test substrate, the exposureapparatus is operated with the same exposure conditions, so that thestructure-size-dependent positioning errors are identical.

In a further embodiment, the multiple arrangement of the first teststructure is arranged in column-type fashion, so that when the teststructure is transferred into the resist layer of the test substrate bythe wafer scanner, the first positioning errors and the secondpositioning errors and the relative positioning errors of the teststructure are determined along an exposure slit of the wafer scanner.

In accordance with this procedure, the multiple arrangement of the firsttest structure along the exposure slit of the wafer scanner becomespossible. The dimensions of the test structure can be relatively smallerthan those of the first pattern. Consequently, the exposure field iscovered by the multiple arrangement during projection of the firstpattern. The first positioning errors and the second positioning errorsare determined over the entire exposure field. This results in a simpledetermination of the first and second positioning errors for differentdimensions of the first pattern.

In a further embodiment, the multiple arrangement of the first teststructure is arranged in matrix-type fashion, so that when the teststructure is transferred into the resist layer of the test substrate bythe wafer stepper, the first positioning errors and the secondpositioning errors of the test structure are determined in the imagingregion of the wafer stepper. The first test structure is arranged in apartial field of the entire exposure field of the wafer stepper. Thedimensions of the test structure can be selected relatively smaller thanthose of the first pattern. Consequently, the exposure field is coveredby the multiple arrangement during projection of the first pattern andthe first positioning errors and the second positioning errors aredetermined over the entire exposure field. This results in a simpledetermination of the first and second positioning errors for differentdimensions of the first pattern.

In a further embodiment, the first micro-patterned alignment mark isformed with a plurality of microstructure elements, so that thepatterning of the first micro-patterned alignment mark corresponds tothe patterning of the first pattern. The micro-patterned alignment markthus has the same structure-size-dependent positioning error as thefirst structure elements.

Since the size of the positioning errors and the dimensions of the firststructure elements are often of the same order of magnitude, a verydensely packed structure can be measured only with difficulty,particularly when a scanning electron microscope is used, sinceassignment errors can occur in the densely packed field of the structureelements. To avoid this problem, a micro-patterned measurement mark isused.

In a further embodiment, providing the correction function includesproviding a model of the photolithographic projection by the exposureapparatus. The model specifies the first positioning error and thesecond positioning error for a multiplicity of positions within theexposure field.

In lithography, models of the photolithographic projection by theexposure apparatus are often used, for example, to optimize the exposureconditions with regard to the resolution that can be achieved. Accordingto the invention, this model is used to determine the first positioningerrors and second positioning errors. This enables a simpledetermination of the correction function since already existing modelcalculations can continue to be used.

In a further embodiment, determining the average relative positioningerror includes forming the difference between the first positioningerror and the second positioning error for a plurality of positionswithin the exposure field, which are subsequently averaged.

The use of the correction values for the exposure apparatus usuallyeffects a correction for the entire exposure field since differentadaptations are not possible within the exposure field. The inventionaccounts for this by calculating an average value.

In a further embodiment, the method further includes providing a secondpattern having a plurality of second structure elements and a pluralityof second measurement marks for forming a respective overlay target withone of the first measurement marks of the first pattern,photolithographic projection of the second pattern by the exposureapparatus into the exposure fields, and determining offset values of theoverlay targets. In the case of projection by the exposure apparatus,the second structure elements are beset by a third positioning errordepending on the dimensions of the second structure elements and theposition of the second structure elements in the exposure field. Thesecond measurement marks are beset by a fourth positioning errordepending on the dimensions of the second measurement marks anddepending on the position of the second measurement marks in theexposure field. Different positioning errors are brought about for thesecond structure elements and second measurement marks due to differentdimensions as a result of aberration. The offset value is composed of anoverlay error, the first positioning error, the second positioningerror, the third positioning error, and the fourth positioning error.

The present invention can extended to a plurality of layers withdifferent patterns. The second pattern includes structure elements and aplurality of second measurement marks that form a respective overlaytarget with a first measurement mark of the first pattern. In additionto correcting the structure-dependent positioning errors of the firstpattern and the first measurement marks, offset values are determinedfor the overlay targets. These offset values are corrected bycontribution of the respective differences between the structureelements and the measurement marks. As a result, thestructure-size-dependent positioning error of the first structureelements with respect to the second structure elements is improved,which leads to an improved overlay during the lithographic projection ofthe patterns.

In a further embodiment, providing the second pattern includes thesecond structure elements having minimal dimensions of 100 nm or less.As already mentioned above, modern production processes have minimalstructure dimensions of less than 100 nm. These critical dimensions aredifferent from the dimensions usually used for measurement marks, sothat the invention can correct the structure-size-dependent positioningerrors particularly in modern technologies with very small dimensions.

In a further embodiment, providing the correction function includes thecorrection function specifying the third positioning error and thefourth positioning error. The correction function is extended to theeffect that the structure-size-dependent positioning errors of thesecond pattern are also specified. The invention can thus be extended ina simple manner to patterns having different minimal dimensions.

In a further embodiment, determining the offset value of the overlaytarget includes providing the first positioning errors as a function ofthe position on the exposure field, providing the third positioningerrors as a function of the position on the exposure field, determiningthe difference between the first positioning error and the thirdpositioning error as a function of the position on the exposure field,determining a first linear function that represents the firstpositioning error as a function of the position on the exposure field,determining a second linear function that represents the thirdpositioning error as a function of the position on the exposure field,and determining further parameters for the simulation model. The furtherparameters are selected based on the first linear function and thesecond linear function such that the difference between the firstpositioning error and the third positioning error as a function of theposition on the exposure field becomes minimal.

Usually, the positioning errors dependent on the position in theexposure field are described relatively accurately by a linear function.To improve the overlay of the first pattern and the second pattern, thedifference between the first positioning error and the third positioningerror is considered as a function of the position on the exposure field.This difference is minimized as the parameters of the simulation modelfor the exposure apparatus are derived from the first linear functionand second linear function, and transmitted to the exposure apparatus.In the case of an exposure, the first and second patterns are optimizedwith regard to the overlay of the first and second structure elementsand the overlay of the first and second measurement marks with respectto one another is not improved, in contrast to what has often beencustomary heretofore.

In a further embodiment, determining the offset value of the overlaytarget includes that the further parameters are allocated to a firstcontribution, which represents a further translation error, and a secondcontribution, which represents a further field rotation error, in the xdirection and/or y direction.

It is often the case in the lithography of two patterns that only onedirection is critical for the overlay. According to the invention, thefurther parameters of the simulation model can be specified in twodirections. Since, the corrections are relatively identical for theexposure fields, the further parameters are allocated to a translationerror or rotation error of the intra-field components of the calculationspecification in order, in the case of an exposure, to improve the firstand second patterns with regard to the overlay of the first and secondstructure elements.

In a further embodiment, determining further parameters for thesimulation model includes transmitting the further parameters to theexposure apparatus, so that these parameters are implemented insubsequent exposures with an improved overlay.

The further parameters determined by the method according to theinvention are often transmitted to the exposure apparatus by an AdvancedProcess Control (APC) control loop during fabrication of integratedcircuits. The invention can thus be applied relatively cost-effectivelyin already existing production installations.

In a further aspect of the invention, a method for correctingstructure-size-dependent positioning errors during the photolithographicprojection by an exposure apparatus includes providing an exposureapparatus suitable for performing an exposure in a plurality of exposurefields, providing one or more movable lens elements in the projectionobjective of the exposure apparatus, in order to correct imagingproperties of the exposure apparatus, providing a simulation model ofthe exposure apparatus, providing a first pattern having a plurality offirst structure elements, providing a correction function for specifyingthe first positioning error, providing an at least second-orderpolynomial having a plurality of parameters, adapting the parameters ofthe polynomial in order to represent the first positioning error as afunction of the position on the exposure field, calculating firstcorrection values for control of the exposure apparatus based on theparameters characterizing the linear portion of the polynomial by thesimulation model, calculating second correction values for the controlof the exposure apparatus based on the parameters characterizing thenonlinear portion of the polynomial by the simulation model,transmitting the first correction values to the exposure apparatus, andtransmitting the second correction values to the movable lens elementsof the exposure apparatus, so that subsequent exposures are performedwith an improved overlay. The simulation model includes a calculationspecification and specifies correction values for intra-field errorsduring the exposure. In the case of projection by the exposureapparatus, the first structure elements are beset by a first positioningerror depending on the dimensions of the first structure elements andthe position of the first structure elements in the exposure field.

In accordance with this procedure, the positioning errors induced byaberration errors based on the nonlinear corrections are improved. Thefirst positioning error is minimized by the nonlinear corrections, whichcan be performed by the movable lens elements of the projectionapparatus.

A method of using the invention for the lithographic patterning of asemiconductor wafer further includes providing the semiconductor wafer,transferring the first pattern by the exposure apparatus byphotolithographic projection into a first layer, and transferring thesecond pattern by the exposure apparatus by photolithographic projectioninto a second layer. The further parameters are transmitted to theexposure apparatus, so that these are implemented in subsequentexposures with an improved overlay. The overlay of two layers withrespect to one another can be improved, which leads to improved productyield in the fabrication of integrated circuits.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be explained in more detail with reference to theaccompanying drawings, in which:

FIG. 1 is a schematic cross-sectional view of an exposure apparatus forapplying the method according to the invention;

FIG. 2 is a schematic cross-sectional view of an overlay measuringapparatus for applying the method according to the invention;

FIG. 3 is a schematic plan view of the front side of a semiconductorwafer during application of the method according to the invention;

FIG. 4 is a schematic plan view of the front side of a semiconductorwafer with an exposure field during the application of the methodaccording to the invention;

FIG. 5 diagrammatically illustrates offset values determined duringapplication of the method according to the invention;

FIG. 6 diagrammatically illustrates offset values determined duringapplication of the method according to the invention;

FIGS. 7A and 7B diagrammatically illustrate offset values determined ina first exposure mode;

FIGS. 8A and 8B diagrammatically illustrate offset values determined ina second exposure mode;

FIG. 9 diagrammatically illustrate measured offset values and functionsadapted thereto in accordance with a further aspect of the invention;and

FIG. 10 diagrammatically illustrates deviations of the measured offsetvalues and the functions adapted thereto in accordance with the furtheraspect of the invention.

DETAILED DESCRIPTION

A method for an exposure in an exposure field of a first and a secondlayer using a wafer scanner during fabrication of random access memorycomponents (DRAM) can also be applied to a plurality of circuit layerswith different exposure apparatuses. Also, the method can be used in thelithographic patterning of layers of other semiconductor components, forexample, in the fabrication of logic circuits or the like.

FIG. 1 shows the construction of an exposure apparatus or projectionapparatus 5 in a schematic cross-sectional view. The projectionapparatus 5 includes a movable substrate holder 12. A semiconductorwafer 10 is placed on the substrate holder 12. A resist layer 14 isapplied to the wafer on a front side, for example, by spinning-on.

The projection apparatus 5 further includes a light source 16 arrangedabove the substrate holder 12 for emitting light, for example, having awavelength of 248 nm, 193 nm, or 157 nm. The light emitted by the lightsource 16 is projected through a projection objective 20 onto thesurface of the semiconductor wafer 10.

A reticle 18 provided with a first pattern of a circuit layer is fittedbetween the light source 16 and the projection objective 20. In the caseof a wafer scanner, an exposure slit is fitted between the reticle 18and the projection objective 20 (not shown in FIG. 1). Through controlof the substrate holder 12, the front side of the semiconductor wafer 10is progressively patterned in individual exposure fields.

For the pattern, for example, a circuit design of a dynamicsemiconductor memory having memory cells with trench capacitors ofminimal dimensions of 100 nm or less in the region of the trenchcapacitors is provided.

As shown in FIG. 1, the projection objective 20 of the projectionapparatus 5 includes a plurality of further elements. A first lenselement 19 and a second lens element 21 are illustrated, for example, inFIG. 1. The first lens element 19 and the second lens element 21 arefitted, e.g., in the beam path between the reticle 18 and thesemiconductor wafer 10 above and respectively below the projectionobjective 20. The first lens element 19 and the second lens element 21correct imaging errors of the lens of the projection objective 20.

As mentioned in the introduction, several types of distortions that leadto imaging errors are known. The exposure apparatus manufacturersattempt to correct the distortions of the lens of the projectionobjective 20 by various correction elements to minimize aberrationerrors for a specific type of exposure, for example, annular exposure ordipole exposure. The specific aberration error characterizing a specificexposure apparatus is measured, for example, by an interferometric phasemeasuring apparatus.

The measured aberration error normally depends on the position of themeasurement point within the exposure field (in the case of a waferstepper) or the exposure slit (in the case of a wafer scanner). Thistwo-dimensional profile of the aberration error is usually described bythe Zernike polynomials, which represent a mathematical model of theprojection objective 20 based on the fact that the aberration functioncan be represented as a superposition of the Zernike polynomials. Eachindividual Zernike polynomial is assigned a polynomial with a specificordinal number. The proportion of the aberration error made up by aspecific order is usually represented by the Zernike coefficients.

Each Zernike coefficient thus corresponds to a specific order of theZernike polynomial and can be assigned to a specific type of aberrationerror. Thus, for example, the Zernike polynomial with the ordinal number4 represents the influence of lack of depth of focus. The Zernikepolynomial with the ordinal number 6 represents astigmatism possiblypresent.

Generally, the first lens element 19 and the second lens element 21 areassigned optical transmission properties that can be altered bydisplacing the first lens element 19 and second lens element 21 suchthat specific nonlinear corrections of, for example, the second or thirdorder can be performed.

FIG. 2 shows the construction of an overlay measuring apparatus 22 in aschematic cross-sectional view. After the photolithographic projection,the positional accuracy of the currently exposed layer relative toalready existing layers is determined by the overlay measuring apparatus22. For this purpose, the first pattern that has already beentransferred into a layer or the substrate has been provided withmeasurement marks suitable for forming an overlay target together withmeasurement marks of a second pattern. The overlay measuring apparatus22 includes a further substrate holder 24 suitable for receiving thesemiconductor wafer 10.

A resist structure 14′ is applied on the front side of the semiconductorwafer 10, the resist structure having arisen through development fromthe resist layer 14. The overlay measuring apparatus 22 furthermoreincludes a further light source 26 in order to irradiate the front sideof the semiconductor wafer 10 with light. The light reflected from thefront side of the semiconductor wafer 10 is detected in a microscope 28connected to a processing means, for example, a processor 30.

Measurement data of overlay targets of the individual exposure fieldsare processed by the microscope 28 and the processor 30. The evaluatedmeasurement results are subsequently transmitted to the projectionapparatus 5. This is usually done by the automatic process control (APCloop) in order to carry out subsequent exposures with the aid of theevaluated measurement results with an improved overlay.

This forms the starting point for the method according to the invention.The text below describes a first embodiment of the invention, in whichthe measurement data of the overlay target for each layer are providedwith a structure-size-dependent correction, which are transmitted to theprojection apparatus 5 in the context of the APC loop.

The starting point is the reticle 18, which is provided with a firstpattern 46. The first pattern 46 has a plurality of first structureelements 48 and a plurality of first measurement marks 44. As shown inFIG. 3, the first structure elements 48 of the first pattern 46 aresurrounded by a rectangular sawing frame 50. The first measurement marks44 are arranged in a corner and in the center of the sawing frame 50.

In the case of a projection by the exposure apparatus 5, the firststructure elements 48 are beset by a first positioning error dependenton the dimensions of the first structure elements 48 and the position ofthe first structure elements 48 in the exposure field 40. However, thefirst positioning error is also dependent on the exposure conditions,for example, the type of illumination in the exposure apparatus 5. Thus,the dependence on the structure size normally changes in the event of achange from dipole, quad-pole, or annular exposure.

In the case of a projection, the first measurement marks 44 are beset bya second positioning error dependent on the dimensions of the firstmeasurement marks 44, the position of the first measurement marks 44 inthe exposure field, and the exposure conditions.

In FIG. 3, the offset values 52 are depicted, for example, for each ofthe overlay targets 42 designated by the position P1, P2, P3. The offsetvalues can be decomposed into a component in the x direction and acomponent in the y direction. Each offset value 52 has an overlay error54 and a relative positioning error 56. The overlay error 54 specifiesthe actual positional inaccuracy of a layer.

The relative positioning error 56 is caused by thestructure-size-dependent incorrect positioning due to lens aberrationand includes the difference between the first and second positioningerrors. According to the invention, this contribution is reduced inorder to achieve an improved overlay.

FIG. 4 shows the result of a simulation calculation of the firstpositioning errors 58 and second positioning errors 60, in which thefirst structure elements 42 have dimensions of approximately 100 nm.Box-in-box structures having external dimensions of approximately 50 μmand a line width of approximately 2 μm have been assumed for the firstmeasurement marks 44. The photolithographic projection is effected by awafer scanner as projection apparatus 5. The first positioning errors 58and second positioning errors 60 are specified along an exposure slit ofthe wafer scanner.

Under the selected exposure conditions of the exposure apparatus 5, thefirst positioning error 58 and the second positioning error 60 deviatefrom one another by up to 6 nm. For illustration, the difference 62between the first positioning error 58 and second positioning error 60is likewise depicted in FIG. 4.

The simulation could be carried out, for example, using the ProLithsimulator from the company KLA-Tencor or the simulator designated asSolid-C for photolithography from the company Sigma-C. Other simulationprograms known to the person skilled in the art can likewise be used.

The result of the simulation calculation provides a correction functionthat specifies the first positioning error 58 and the second positioningerror 60 as a function of the position along the exposure slit. Anaverage relative positioning error is determined from the firstpositioning error 58 and the second positioning error 60, and specifiesthe difference between the first positioning error 58 and the secondpositioning error 60 in averaged fashion along the exposure slit. In theabove example, the average relative positioning error would beapproximately −3 nm.

This value of the average relative positioning error specifies themagnitude of the average incorrect positioning along the exposure slitthat occurs during the determination of the position of the firstmeasurement marks 44 relative to the first structure elements 42. Inorder to be able to correct this error during subsequent exposures, thevalue of the average relative positioning error is transmitted to theexposure apparatus 5 as intra-field correction.

A further possibility for determining the correction function isobtained by a test exposure of a test substrate with a test patterncomprising parts of the first pattern 46. After providing the testsubstrate with a resist layer on the front side, the test mask with thetest pattern is introduced into the projection apparatus 5. The testpattern has a multiple arrangement of a first test structure. The firsttest structure includes the first pattern 46, the plurality of firstmeasurement marks 44, and at least one first micro-patterned alignmentmark. The test pattern is transferred into the resist layer of the testsubstrate by photolithographic projection. The values of the firstpositioning error 58 of the first pattern 46 relative to the firstmeasurement marks 44 and the at least one first micro-patternedalignment mark are subsequently determined for each element of the firstmultiple arrangement.

If a wafer scanner is provided as the exposure apparatus 5, the multiplearrangement of the first test structure is preferably arranged incolumn-type fashion, so that when the test structure is transferred intothe resist layer of the test substrate, the first positioning errors 58,and the second positioning errors 60 of the test structure from whichthe relative positioning errors are calculated are determined along theexposure slit of the wafer scanner.

If a wafer stepper is provided as the exposure apparatus 5, the multiplearrangement of the first test structure is preferably arranged inmatrix-type fashion, so that when the test structure is transferred intothe resist layer of the test substrate by the wafer stepper, the firstpositioning errors 58 and the second positioning errors 60 of the teststructure can be determined in the imaging region of the wafer stepper.

The first micro-patterned alignment mark is formed with a plurality ofmicrostructure elements, so that the patterning of the firstmicro-patterned alignment mark corresponds to the patterning of thefirst structure elements 48 of the first pattern 46. As a result, thefirst micro-patterned alignment mark has the same aberration error asthe first structure elements 48.

The correction of the first positioning errors 58 and of the secondpositioning errors 60 is performed in particular for each critical layerof the semiconductor wafer prior to the photolithographic projection.The method according to the invention is performed for the layers havingminimal structure dimensions in the vicinity of the resolution limit ofthe projection apparatus 5 and small overlay tolerances with respect tooverlying or underlying layers. An improved overlay of different layersof a semiconductor wafer is produced overall.

As is explained below, the overlay of different layers of asemiconductor wafer can be improved, if the positioning errors inducedby aberration are optimized not only for each layer individually, butrather in each case together, e.g., in pairs, for layers that arecritical with regard to the overlay.

The starting point of this further embodiment of the invention is asecond pattern, which is patterned with improved overlay above the firstpattern 46 into a layer of the semiconductor wafer in the case ofphotolithographic projection. The second pattern has a plurality ofsecond structure elements and a plurality of second measurement marksfor forming the respective overlay target 42 with one of the firstmeasurement marks of the first pattern. In the case of projection by theexposure apparatus, the second structure elements are beset by a thirdpositioning error depending on the dimensions of the second structureelements and the position of the second structure elements in theexposure field. The second structure elements have, for example, minimaldimensions of 100 nm or less.

In the case of a projection, the second measurement marks are beset by afourth positioning error dependent on the dimensions of the secondmeasurement marks and dependent on the position of the secondmeasurement marks in the exposure field. The second measurement marksare provided, for example, in the form of a frame having an externaldimension of approximately 50 μm and a line width of 2 μm. The secondpattern is surrounded by a further sawing frame. The second measurementmarks are arranged such that a second measurement mark lies in theregion of the corner of the further sawing frame. A second measurementmark may also be arranged in the region of the midpoint of the furthersawing frame.

After the photolithographic patterning, offset values of the overlaytargets are determined by the overlay measuring apparatus 22. The offsetvalue includes an overlay error, the first positioning error 58, thesecond positioning error 60, the third positioning error, and the fourthpositioning error.

The correction function discussed in connection with the first exemplaryembodiment is modified for specifying the third positioning error andthe fourth positioning error.

This may be effected, as already explained above, either by a simulationof the photolithographic projection. The simulation is carried out withthe dimensions of the second structure elements and the secondmeasurement marks.

A further test substrate and a further test mask can be provided todetermine the third positioning errors and the fourth positioning errorson the basis of a test exposure. In this case, the dimensions of thepattern on the further test mask correspond to the dimensions of thesecond structure elements and the second measurement marks.

To improve the overlay of the offset value of the overlay targets 44,the first positioning error 58 is provided as a function of the positionon the exposure field, as explained above, either by a simulationcalculation or exposure of a test substrate.

FIG. 5 shows the first positioning error 58 along a coordinatedirection. As shown in FIG. 5, the third positioning error 64 is thenprovided as a function of the position on the exposure field and thedifference 72 between the first positioning error 58 and the thirdpositioning error 64 as a function of the position on the exposure fieldis plotted as a further curve.

Instead of the above-explained averaging of the first positioning error58 over the exposure field or, in the case where a wafer scanner isused, the exposure slit, a first linear function is determinedhereinafter, which represents the first positioning error as a functionof the position on the exposure field. As shown in FIG. 6, the firstpositioning error 58 follows a profile which can be approximated by thefirst linear function with sufficient accuracy. The first linearfunction 68 is likewise depicted in FIG. 5.

A second linear function 70 is subsequently determined, which,analogously to the first linear function 68, represents the thirdpositioning error 64 as a function of the position on the exposurefield. The second linear function 68 is shown in FIG. 6.

The first linear function 68 and the second linear function 70 are usedhereinafter for determining further parameters for the simulation model.The further parameters chosen based on the first linear function 68 andthe second linear function 70 such that the difference 72 between thefirst positioning error 58 and the third positioning error 62 as afunction of the position on the exposure field becomes minimal.

The further parameters are allocated to a first contribution, whichrepresents a further translation error, and a second contribution, whichrepresents a further field rotation error, and are determined separatelyin a first direction and a second direction (y direction) arrangedrelatively perpendicular to the first direction (e.g., x direction). Thelayers of an integrated circuit that are critical for the overlay areoften sensitive to overlay errors only in one direction, so thatdivision into two directions facilitates the evaluation of the offsetvalues 52. For each layer, the first positioning error is correctedusing a linear function F(y),F(y)=a+b*y.

The linear function is adapted to the profile of the first and secondpositioning errors along the position y of the exposure slit in order todetermine the free parameters thereof, namely the gradient b and theconstant term a. The two parameters are returned as intra-field errorsto the exposure apparatus by an APC loop. The first parameter acorresponds to the field magnification error and the second parameter bcorresponds to the translation error of the overlay model.

These parameters of the simulation model are transmitted to the exposureapparatus 5 for each layer, so that, in the case of subsequentexposures, these are implemented with an improved overlay. The result ofthis procedure is shown in FIG. 6.

FIG. 6 shows, in addition to the first positioning error 58 and thethird positioning error 62, the improved overlay between the firststructure elements and second structure elements as curve 74. Forcomparison, a conventional correction of the overlay targets, in thecase of which structure-size-dependent positioning errors are not takeninto consideration, is plotted as further curve 76. The improvementamounts to approximately 55% averaged over the exposure slit, whichresults in a significantly higher product yield particularly in theproduction of integrated circuits.

As is explained below, a further improvement of the positioning errorcan be achieved using the first correction lens elements 19 and thesecond correction lens elements 21 of the exposure apparatus 5. This isimportant particularly when exposure conditions of the projectionapparatus 5 bring about nonlinear aberration errors along the exposureslit which in turn lead to nonlinear structure-size-dependentpositioning errors of the structure elements or measurement marks.

FIG. 7A shows in a diagram the profile of the first positioning error 58of the first pattern 46 of the first structure elements 48 as a functionof the position y along the exposure slit of the projection apparatus 5.This profile is determined, for example, by a simulation, as describedabove. It is assumed for the simulation that a halftone phase mask isused as reticle 18 and the light source 16 performs a so-called dipoleexposure.

As shown in FIG. 7A, the first positioning error 58 exhibits a change bymore than 6 nm, for example, at a position that deviates byapproximately 5 mm from the midpoint of the exposure slit.

FIG. 7B shows the second positioning error 60 for the measurement mark42 as a function of the position of the exposure slit of projectionapparatuses. A nonlinear profile of the second positioning error 60 canbe discerned in this case.

The profile of the positioning errors of the structure elements and ofthe overlay targets changes with different exposure conditions, as isshown in connection with FIGS. 8A and 8B. FIGS. 8A and 8B show the firstpositioning error 58 and the second positioning error 60 for an annularexposure using a halftone phase mask. It can be seen that the profile ofthe positioning errors is different from those of the dipole exposure inaccordance with FIGS. 7A and 7B.

As explained above in connection with FIG. 6, the positioning error ispreviously corrected using a linear functionF(y)=a+b*y.

The linear function is adapted to the profile of the positioning errorsalong the position y of the exposure slit in order to determine the freeparameters, the gradient b and the constant term a. The two parametersare returned as intra-field errors to the exposure apparatus in thecontext of the APC loop. The first parameter corresponds to the fieldmagnification error and the second parameter corresponds to thetranslation error of the overlay model.

FIGS. 7A and 7B show that the value of the positioning error for thefirst structure elements and the overlay targets varies continuouslyalong the exposure slit. However, a correction effected based on alinear function leads to non-correctable positioning errors. In order tominimize the overlay error 54, a nonlinear correction of the firstpositioning error 58 of the first structure elements 48 along theexposure slit is hereinafter performed. This is explained in more detailin connection with FIG. 9. FIG. 9 shows the profile of the firstpositioning error 58 as data points along the exposure slit. The firstpositioning error 58 is specified relative to an ideal position in FIG.9. The ideal position may be effected, for example, based on acalculation, as specified above, or a measurement. However, the positionof an already patterned preliminary layer to be optimized with regard toits overlay with respect to the layer currently being projected may alsobe considered for the ideal position.

In FIG. 9, the measurement points are connected by a broken line 80. Alinear correction function 82 determined by an adaptation to the datavalues is depicted for comparison. It can be seen that only a limitedaccuracy can be achieved in the adaptation by a linear function.

This is illustrated once again in FIG. 10, which specifies thedifference 84 between the data points and the value of the linearfunction as a function of the position along the exposure slit. Itfollows from FIG. 10 that large deviations result in particular at theedge and in the center of the exposure slit.

In comparison with this, FIG. 9 shows a second-order polynomial 86 and athird-order polynomial 88. The second-order polynomial is represented bythe relationshipF(y)=a+b*y+c*y ²and the third-order polynomial is correspondingly represented byF(y)=a+b*y+c*y ² +d*y ³.Both polynomials are hereinafter adapted to the profile of the datapoints. Both curves reproduce the profile of the data points relativelybetter. This can be seen, in particular, in FIG. 10, since thedifference values (90) between the second-order polynomial and thedifference values (92) between the third-order polynomial and the datapoints are relatively significantly smaller.

The coefficients a and b of the second-order polynomial and of thethird-order polynomial may again be assigned directly to the correctionparameters of the overlay model (translation and field magnificationerrors of the intra-field correction).

The higher-order terms, i.e., the coefficient c in the case of thesecond-order polynomial and c and d in the case of the third-orderpolynomial, are used as correction values for the control of thecorresponding lens elements of the correction lenses 19, 21. For thispurpose, the coefficients are assigned to a distortion described bycorresponding Zernike coefficients. The degree and extent of thecorrection of a corresponding movable lens element 19 or 21 aredetermined based on the lens model. In this way, it is possible to carryout nonlinear corrections along the exposure slit with the aid of thelens elements 19, 21.

In accordance with this procedure, it is possible to achieve asignificant improvement of the positioning errors induced by aberrationerrors on the basis of the nonlinear corrections. As a result of thesenonlinear corrections which can be performed by the lens elements 19,21, the first positioning error 58 is minimized in comparison with theideal position.

However, an alteration of the lens elements 19, 21 may also bring aboutan alteration of the imaging properties of the projection apparatus 5,so that the improvement of the aberration errors and the possibleimpairment of the imaging properties have to be balanced.

The above example discussed the possibility of using the movable lenselements 19, 21 for improving the correction of the aberration errors.However, it is also conceivable to obtain an adaptation betweendifferent exposure apparatuses 5 by the movable lens elements 19, 21, asis explained below.

In high-volume process lines of DRAM fabrication, different exposureapparatuses are often used for lithographic patterning of identicallayers in order to obtain a highest possible throughput of thefabrication installation. Since the aberration error constitutes anindividual property of the lens (or lens system) of the projectionobjective 20, different aberration errors are also to be expected fordifferent exposure apparatuses.

FIGS. 7A, 7B, 8A, and 8B each illustrate a further first positioningerror 58′ and a further second positioning error 60′ which occur whenanother exposure apparatus is used. A different profile of thepositioning errors along the exposure slit results for differentexposure apparatuses, as shown in the corresponding figures. Whendifferent exposure apparatuses are used, each exposure apparatus hasavailable a set of movable lens elements 19, 21, which, analogously tothe above explanations, can be adapted such that the overlay of twosubsequently patterned layers is improved.

To summarize, a plurality of implementations can achieve a correction ofthe positioning errors brought about by aberration of the projectionobjective by not only evaluating the overlay targets, as has beencustomary heretofore, but also accounting for thestructure-size-dependent positioning errors of the circuit pattern. Itis possible to improve the overlay of different layers in the productionof integrated circuits, thereby achieving an improvement of the numberof functional circuits.

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be apparent to one skilled in theart that various changes and modifications can be made therein withoutdeparting from the spirit and scope thereof. For example, some or all ofthe subject matter may be embodied as software, hardware or acombination thereof. Accordingly, it is intended that the presentinvention covers the modifications and variations of this inventionprovided they come within the scope of the appended claims and theirequivalents.

List of reference symbols  5 Projection apparatus 10 Semiconductor wafer12 Substrate holder 14 Resist layer 14′ Resist structure 16 Light source18 Reticle 20 Projection objective 22 Overlay measuring apparatus 24Further substrate holder 26 Further light source 28 Microscope 30Processing means 40 Exposure field 42 Overlay target 44 Firstmeasurement mark 46 First pattern 48 First structure elements 50 Sawingframe 52 Offset value 54 Overlay error 56 Relative positioning error 58First positioning error 60 Second positioning error 62 Differencebetween first and second positioning error 64 Third positioning error 66Fourth positioning error 68 First linear function 70 Second linearfunction 72 Difference between first and third positioning error 74Curve 76 Further curve 80 Data points 82 Linear function 86 Second-orderpolynomial 88 Third-order polynomial 84, 90, 92 Deviation

1. A method for the correction of structure size dependent positioningerrors during the photolithographic projection by an exposure apparatus,the method comprising: providing an exposure apparatus for performing anexposure in a plurality of exposure fields; providing a simulation modelof the exposure apparatus with a calculation specification forspecifying correction values for intra-field errors during the exposure;providing a first pattern including a plurality of first structureelements and a plurality of first measurement marks;photolithographically projecting the first pattern by the exposureapparatus into the exposure fields, different positioning errors beingbrought about for the first structure elements and first measurementmarks due to different dimensions as a result of aberration, the firststructure elements being beset by a first positioning error depending onthe dimensions of the first structure elements and the position of thefirst structure elements in the exposure field, the first measurementmarks being beset by a second positioning error depending on thedimensions of the first measurement marks and the position of the firstmeasurement marks in the exposure field; providing a correction functionfor specifying the first positioning error and the second positioningerror; determining an average relative positioning error from the firstpositioning error and the second positioning error; calculatingcorrection values for the control of the exposure apparatus based on thefirst positioning error and the second positioning error by thesimulation model; and transmitting the correction values as anintra-field correction to the exposure apparatus so that subsequentexposures are performed with an improved overlay.
 2. The method asclaimed in claim 1, wherein providing the first pattern includes thefirst structure elements having minimal dimensions of 100 nm or less. 3.The method as claimed in claim 1, wherein providing the first patternincludes the first measurement marks having minimal dimensions ofbetween 0.5 μm and 5 μm and forming the first part of an overlay target.4. The method as claimed in claim 3, wherein providing the first patternincludes the first measurement marks having the form of a frame with anexternal dimension of approximately 50 μm and a line width ofapproximately 2 μm.
 5. The method as claimed in claim 1, whereinproviding the first pattern comprises: providing a sawing framesurrounding the first pattern; and providing the plurality of firstmeasurement marks arranged such that a respective first measurement marklies in the region of each corner of the sawing frame.
 6. The method asclaimed in claim 5, wherein providing the first pattern further includesproviding the plurality of first measurement marks arranged such that atleast one first measurement mark lies in the region of the midpoint ofthe exposure field.
 7. The method as claimed in claim 1, whereinproviding the correction function includes providing a test substratewith a resist layer on the front side; providing a first test mask witha first test pattern having a first multiple arrangement of a first teststructure, the first test structure including the first pattern, theplurality of first measurement marks, and at least one firstmicro-patterned alignment mark; transferring the first test pattern byphotolithographic projection into the resist layer of the testsubstrate; and determining the values of the first positioning error ofthe first pattern relative to the at least one first measurement markand the at least one first micro-patterned alignment mark for eachelement of the first multiple arrangement.
 8. The method as claimed inclaim 7, wherein the exposure apparatus is a wafer scanner.
 9. Themethod as claimed in claim 8, wherein the multiple arrangement of thefirst test structure is arranged in column-type fashion, so that whenthe test structure is transferred into the resist layer of the testsubstrate by the wafer scanner, the first positioning errors and thesecond positioning errors and the relative positioning errors of thetest structure are determined along an exposure slit of the waferscanner.
 10. The method as claimed in claim 7, wherein the exposureapparatus is a wafer stepper.
 11. The method as claimed in claim 10,wherein the multiple arrangement of the first test structure is arrangedin matrix-type fashion, so that when the test structure is transferredinto the resist layer of the test substrate by the wafer stepper, thefirst positioning errors and the second positioning errors of the teststructure are determined in the imaging region of the wafer stepper. 12.The method as claimed in claim 7, wherein the first micro-patternedalignment mark is formed with a plurality of microstructure elements, sothat patterning of the first micro-patterned alignment mark correspondsto patterning of the first structure elements of the first pattern. 13.The method as claimed in claim 1, wherein providing the correctionfunction includes providing a model of the photolithographic projectionby the exposure apparatus for specifying the first positioning error andthe second positioning error for a plurality of positions within theexposure field.
 14. The method as claimed in claim 13, wherein the modelof the photolithographic projection by the exposure apparatus isgenerated via a simulator.
 15. The method as claimed in claim 9, whereindetermining the average relative positioning error includes determiningthe difference between the first positioning error and the secondpositioning error for a plurality of positions within the exposurefield, the differences subsequently being averaged.
 16. The method asclaimed in claim 15, wherein determining the average relativepositioning error includes forming the difference between the firstpositioning error and the second positioning error along the exposureslit.
 17. The method as claimed in claim 1, further comprising:providing a second pattern including a plurality of second structureelements and a plurality of second measurement marks for forming arespective overlay target with one of the first measurement marks of thefirst pattern, photolithographically projecting the second pattern bythe exposure apparatus into the exposure fields, different positioningerrors being brought about for the second structure elements and secondmeasurement marks due to different dimensions as a result of aberration,the second structure elements being beset by a third positioning errordepending on the dimensions of the second structure elements and theposition of the second structure elements in the exposure field, thesecond measurement marks being beset by a fourth positioning errordepending on the dimensions of the second measurement marks and theposition of the second measurement marks in the exposure field; anddetermining offset values of the overlay targets, the offset value beingcomposed of an overlay error, the second positioning error, and thefourth positioning error.
 18. The method as claimed in claim 17, whereinproviding the second pattern includes the second structure elementshaving minimal dimensions of 100 nm or less.
 19. The method as claimedin claim 17, wherein providing the second pattern includes the secondmeasurement marks having minimal dimensions of between 0.5 μm and 5 μm.20. The method as claimed in claim 19, wherein providing the secondpattern includes the second measurement marks having the form of a framewith an external dimension of approximately 50 μm and a line width ofapproximately 2 μm.
 21. The method as claimed in claim 17, whereinproviding the second pattern includes: providing a further sawing framesurrounding the second pattern; and providing the second measurementmarks arranged such that a respective second measurement mark lies inthe region of the corner of the further sawing frame and/or a secondmeasurement mark lies in the region of the midpoint of the furthersawing frame.
 22. The method as claimed in claim 17, wherein providingthe correction function includes the correction function specifying thethird positioning error and the fourth positioning error.
 23. The methodas claimed in claim 17, wherein determining the offset value of theoverlay target includes providing the first positioning errors as afunction of the position on the exposure field; providing the thirdpositioning errors as a function of the position on the exposure field;determining the difference between the first positioning error and thethird positioning error as a function of the position on the exposurefield; determining a first linear function that represents the firstpositioning error as a function of the position on the exposure field;determining a second linear function representing the third positioningerror as a function of the position on the exposure field; anddetermining further parameters for the simulation model, the furtherparameters selected based on the first linear function and the secondlinear function such that the difference between the first positioningerror and the third positioning error as a function of the position onthe exposure field becomes minimal.
 24. The method as claimed in claim23, wherein determining the offset value of the overlay target furtherincludes the further parameters being allocated to a first contributionrepresenting a further translation error, and a second contributionrepresenting a further field rotation error, in a first direction and asecond direction.
 25. The method as claimed in claim 23, whereindetermining further parameters for the simulation model furthermoreincludes transmitting the further parameters to the exposure apparatusto be implemented in subsequent exposures with an improved overlay. 26.A method for the correction of structure size dependent positioningerrors during the photolithographic projection by an exposure apparatus,comprising: providing an exposure apparatus for performing an exposurein a plurality of exposure fields, a plurality of first structureelements being beset by a first positioning error depending ondimensions of the first structure elements and the position of the firststructure elements in the exposure field; providing at least one movablelens element in the projection objective of the exposure apparatus tocorrect imaging properties of the exposure apparatus; providing asimulation model of the exposure apparatus with a calculationspecification for specifying correction values for intra-field errorsduring the exposure; providing a first pattern including the pluralityof first structure elements, providing a correction function forspecifying the first positioning error; providing an at leastsecond-order polynomial including a plurality of parameters; adaptingthe parameters of the polynomial to represent the first positioningerror as a function of the position on the exposure field; calculatingfirst correction values for the control of the exposure apparatus basedon parameters characterizing a linear portion of the polynomial by thesimulation model; calculating at least a second correction value for thecontrol of the exposure apparatus based on parameters characterizing anonlinear portion of the polynomial by the simulation model;transmitting the first correction values to the exposure apparatus; andtransmitting the second correction value to the at least one movablelens element of the exposure apparatus so that subsequent exposures areperformed with an improved overlay.
 27. The method as claimed in claim26, wherein providing the first pattern includes the first structureelements having minimal dimensions of 100 nm or less.
 28. The method asclaimed in claim 26, wherein providing the correction function includes:providing a model of the photolithographic projection by the exposureapparatus for specifying the first positioning error and the secondpositioning error for a multiplicity of positions within the exposurefield.
 29. The method as claimed in claim 26, wherein providing thecorrection function includes: providing a test substrate with a resistlayer on the front side; providing a first test mask with a first testpattern having a first multiple arrangement of a first test structure,the first test structure including the first pattern, the plurality offirst measurement marks, and at least one first micro-patternedalignment mark; transferring the first test pattern by photolithographicprojection into the resist layer of the test substrate; and determiningthe values of the first positioning error of the first pattern relativeto the at least one first measurement mark and the at least one firstmicro-patterned alignment mark for each element of the first multiplearrangement.
 30. The method as claimed in claim 29, wherein the exposureapparatus is a wafer scanner.
 31. The method as claimed in claim 30,wherein the multiple arrangement of the first test structure is arrangedin column-type fashion, so that when the test structure is transferredinto the resist layer of the test substrate by the wafer scanner, thefirst positioning errors are determined along an exposure slit of thewafer scanner.
 32. The method as claimed in claim 29, wherein theexposure apparatus is a wafer stepper.
 33. The method as claimed inclaim 32, wherein the multiple arrangement of the first test structureis arranged in matrix-type fashion, so that when the test structure istransferred into the resist layer of the test substrate by the waferstepper, the first positioning errors of the test structure aredetermined in the imaging region of the wafer stepper.
 34. The method asclaimed in claim 29, wherein the first micro-patterned alignment mark isformed with a plurality of microstructure elements, so that thepatterning of the first micro-patterned alignment mark corresponds tothe patterning of the first structure elements of the first pattern. 35.The method as claimed in claim 26, wherein providing the polynomialincludes providing a second- or higher-order polynomial, the parameterscharacterizing a linear portion of the polynomial being derived from aconstant term and a linear term.
 36. The method as claimed in claim 35,wherein providing the polynomial includes the parameter characterizing anonlinear portion of the polynomial is derived from a quadratic orhigher term.
 37. The method as claimed in claim 26, wherein providingthe polynomial includes providing a third-order polynomial.
 38. Themethod as claimed in claim 26, wherein transmitting the secondcorrection values is followed by carrying out a photolithographicprojection of the first pattern by the exposure apparatus into theexposure fields.
 39. The method as claimed in claim 17, wherein theplurality of exposure fields are disposed on a semiconductor wafer, themethod further comprising: providing the semiconductor wafer;transferring the first pattern by the exposure apparatus byphotolithographic projection into a first layer of the semiconductorwafer; and transferring the second pattern by the exposure apparatus byphotolithographic projection into a second layer of the semiconductorwafer.
 40. The method as claimed in claim 26, wherein the plurality ofexposure fields are disposed on a semiconductor wafer, the methodfurther comprising: providing the semiconductor wafer; transferring thefirst pattern by the exposure apparatus by photolithographic projectioninto a first layer of the semiconductor wafer.